Crowdfunding Web sites such as Kickstarter and Indiegogo have proven incredibly effective in uncovering financial backers for new technologies or businesses that might not otherwise gotten off the ground.

The model could also rewrite the rules for funding clean energy projects, particularly rooftop solar installations.

Exhibit A: one pioneer of this concept, Solar Mosaic, raised more than $313,000 this week for four projects that will be installed on affordable housing. In fact, the site raised that money in less than 24 hours.

More than 400 investors put in anywhere from $25 to $30,000 to help get these installations off the ground, with the average investment around $700, the company said.

"We are thrilled at how the public showed up yesterday," said Dan Rosen, Mosaic CEO, in a press release issued the day after the offerings were posted. "It's indicative of a pent-up demand that we are working to meet. People want strong returns and want to know what their money is invested in. Our marketplace allows people to sidestep Wall Street by investing in Main Street."

Since it was launched two years ago, Solar Mosaic has raised more than $1.1 million from 700 investors to back 12 rooftop solar installations in California, Arizona and New Jersey. The latest projects were available to investors in California and New York.

The average annual return on these projects is 4.5 percent, net of the servicing fees, over a period of nine years.

Investor Rosana Francescato noted: "Mosaic is lowering the barrier for regular people like me - not just rich investors or big companies - to benefit from solar power while providing a good return on investment. I invested in several projects, the process was easy and it only took a few minutes.

The company's approach is particularly relevant, given the explosion of rooftop solar across the United States. In the fourth quarter of 2012, residential installations grew 12 percent to hit an all-time high of 118 megawatts, according to data from the Solar Energy Industries Association.